Mice give clue to 'self-repairing skin'

Published:10:23Wednesday 26 September 2012

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“‘Scar free healing’ in mice may give clues to human skin repair,” BBC News has reported. The broadcaster says that scientists are interested in figuring out “how the healing takes place and if it could apply to people”.

While some species are known to be able to regenerate their skin and, in some cases, entire body parts, it is thought that this ability is limited in mammals. However, the researchers who carried out this study had heard reports that a particular mouse called the African spiny mouse does have this ability.

The researchers trapped a number of these mice in central Kenya and took them to a laboratory for further testing. They found that the mice have skin that tears away easily, enabling them to escape predators. The mice regenerate the lost skin, and even grow new hair, instead of forming a scar.

The study challenges some of the conventional wisdom surrounding wound healing and regenerative processes in mammals. It is hoped that new understanding of these biological processes could lead to new treatments for skin damage, scalding and burns in humans. But this research is at a very early stage and whether these processes will one day help the regeneration of human tissue remains to be seen.

The study was carried out by researchers from the Universities of Florida, Wyoming and Nairobi. No information regarding the funding was listed in the publication.

This research was covered quite appropriately by the media, with the BBC being careful to emphasise that “working out what is happening and then trying to transfer the findings to people is likely to be a long journey”.

This was an animal study that examined the wound healing ability of a specific type of mouse, called the African spiny mouse.

Several animals are able to lose (or ‘autotomise’) sections of tissue or whole limbs in order to escape capture by predators. After this tissue is lost, it is either:

This research looked at an unusual example of a mammal – the African spiny mouse – which is capable of regenerating lost tissue instead of simply forming a scar over the wound.

The researchers first set out to confirm anecdotal evidence (unverified ‘word-of-mouth’ reports) that the African spiny mouse does indeed autotomise its skin to evade predators. Once they had done this, they then examined the healing properties of these wounds, studying how quickly they healed as well as the processes involved. They also examined exactly how the tissue regenerated.

While most adult mammals are unable to regenerate skin and associated tissue after being injured, previous studies have shown that a few animals (including rabbits) are able to do so. To see if the African spiny mice exhibited the same capability, the researchers punched 4mm holes in the ears of the mice, and examined what types of tissues were regenerated.

The researchers found that handling of the African spiny mice often led to the tearing away of skin from the back, resulting in large open wounds. These wounds ranged from small areas to the loss of nearly 60% of the skin from the back. The researchers found that these wounds healed quickly, and that the mouse’s characteristic spiny hairs regrew as well, completely covering the wound.

When examining the wound healing process, the researchers found that, as with wound healing in other mammals, a scab formed quickly and bleeding stopped. However, new cells called epithelial cells formed on top of the wound after three days, more quickly than seen in other adult mammals. Also, as is seen in other rodents, the wound healed mainly by contracting, or shrinking the wound size. After 17 days, 95% of the wound closure had been due to this contraction of the tissue.

This is unlike other species, in which a thick web of collagen is laid down over the wound in order to seal it off and protect the body from infection, resulting in scarring. Because the mouse skin healed so quickly, less collagen was deposited, resulting in no visible scarring.

When they examined tissue regeneration after the loss of skin from the back, the researchers found that new skin cells and hair follicles (the cells embedded in the skin, from which hairs grow) were also regenerated in the deposited sections of collagen.

The African spiny mice were able to regenerate the lost ear tissue, growing new skin, hair follicles, fat cells, muscle and cartilage instead of forming scars. This finding was similar to previous results in rabbits.

Finally, during the ear experiment, the researchers found evidence to suggest that the tissue regeneration was due to the formation of a blastema, which is a group of cells that are responsible for the regrowth of lost limbs in salamanders.

The researchers say their results suggest that the African spiny mouse uses a balance of scarring and tissue regeneration in wound healing. They say this “indicates that mammals may have a higher capacity for regenerations than was previously believed”.

This was an early stage animal study that describes an unusual phenomenon in mammal wound healing and provides a basis for future studies. These studies are likely to investigate the molecular processes that underpin the skin and hair regeneration in the African spiny mouse.

The researchers say that future investigations will focus on how the mice are able to control scar formation, and that this may “shed light on how regeneration and scarring can be balanced in the face of infection and inflammation”. They also say that this should allow for further research into tissue regeneration in mammals, and that the African spiny mouse may prove quite useful in finding ways to promote tissue regeneration instead of scarring.

When the molecular pathways that underlie the wound healing processes seen in African spiny mice are more thoroughly understood, researchers may begin to study whether they can be applied to wound healing and regenerative medicine in people. However, it is likely to be a long time until this intriguing piece of research leads to medical applications.